Generally, the present invention relates to a method and device for determining the position of the cutting surface or tip of a cutting tool and, more particularly, to the determination of the position of the cutting tool tip relative to the axis of rotation of a spindle-mounted workpiece without requiring physical contact between the tool and the workpiece.
In the operation of an automated machine tool signals from a computer program or a computer tape are utilized to actuate the slides for displacing the cutting tool along a programmed path to effect the desired machining of the workpiece surface. The program contains commands which are precalculated on the basis that the cutting tip of the cutting tool is in an exact, or known, initial reference position. Therefore, before machining can begin in such automated machine tools, it must be established that the cutting tip of the tool is, in fact, in the reference position since the quality of the machining operation is dependent upon the accuracy of this initial reference position.
Previously, several techniques including the use of feeler gauges, capacitance gauges, spark gaps, and the like, have been used to determine the initial tool position. While such prior art techniques have been somewhat successful, there are certain problems associated with their use which effectively detract from their overall desirability in determining the tool position. For example, the extent the feeler gauge is pinched during the determination of the tool position cannot be readily ascertained so that some error may exist in the determination of the tool position. Also, with the capacitance gauges the particular tool geometry effects the operation of the gauge so as to require frequent recalibration of the gauge to assure accuracy. Other techniques, such as use of a non-contact spark-gap-type system for tool setting such as described in assignee's U.S. Pat. No. 3,524,130, are disadvantageous in some instances due to possible damage by the spark to sharp-pointed cutting tools, such as diamond tools and the like.